This invention relates to base oils and drilling fluids or muds made from such base oils, which are substantially non-toxic, essentially non-polluting, biodegradable and highly useful in low temperature operations.
In pending U.S. application Ser. No. 08/620,983, filed Mar. 22, 1996, supra, there is disclosed base oils which are non-toxic, non-polluting, biodegradable and suitable for use in forming drilling fluid compositions by dispersing therein at least one additive selected from the group consisting of weighting agents, emulsifiers, wetting agents, viscosifiers, fluid loss control agents, proppants and other particulate agents. In forming the drilling fluids a continuous oil phase, or water-in-oil invert emulsion phase (where water or brine is present and emulsified in the solvent), provide a medium for the dispersed additive, or additives. The base oil is constituted of a mixture of normal paraffins (n-paraffins) and isoparaffins having from about 10 to about 24 carbon atoms, i.e., C10-C24 n-paraffins and isoparaffins, preferably C12-C18 paraffins, having an isoparaffin:n-paraffins molar ratio ranging generally from about 0.5:1 to about 9:1, and the isoparaffins of the mixture contain greater than 50 percent, generally 70 percent, by weight of the isoparaffins in the mixture, of mono-methyl species, e.g., 2-methyl, 3-methyl, 4-methyl, xe2x89xa75-methyl or the like, with minimal formation of isoparaffins having branches with substituent groups of carbon number greater than 1, e.g., ethyl, propyl, butyl or the like.
These base oils form high performance drilling fluids of low toxicity, and they are environmentally friendly. Like conventional diesel fuels they form drilling fluids, or muds, which have excellent rheological properties for rotary drilling, but unlike conventional diesel fuels do not pose a serious and costly disposal problem for offshore operators. Thus, with conventional diesel operators must barge spent mud and cuttings to shore for land disposal, because diesel fuel cannot meet U.S. Environmental Protection Agency Standards regarding discharge limitations and/or permit requirements. In contrast, this new base oil admirably meets this need, and provides excellent rheological properties. However, the oil and drilling fluids made from the new base oil is lacking in that it is of low pour point, and its low temperature performance leaves much to be desired. It does not perform well under cold temperature conditions which are frequently encountered in drilling operations, e.g., in Alaskan or North Sea operations. Accordingly, there remains a need for a further improved base oil; and drilling fluid made from such base oil, of low toxicity, biodegradable, and environmentally friendly, but yet will be useful at low temperature conditions.
This invention, which supplies this need and others, accordingly relates to a substantially non-toxic, essentially non-polluting, biodegradable, low temperature base oil, and drilling fluid, or mud composition made by dispersing in said base oil one or more of the weighting agents, emulsifiers, wetting agents, viscosifiers, fluid loss control agents, proppants, and particulate agents are mixed with the paraffinic solvent composition to form an emulsion in which the latter forms a continuous oil phase, or water-in-oil invert emulsion phase.
The base oil is constituted of a mixture of n-paraffins and isoparaffins ranging from about C10 to about C24, preferably from about C12 to about C18, wherein the isoparaffins component of the mixture contains at least about 30 percent, preferably from about 30 percent to about 50 percent, based on the weight of the isoparaffins component in the mixture, of the mono-methyl species (e.g., 2-methyl, 3-methyl, 4-methyl, xe2x89xa75-methyl or the like), and at least 30 percent, preferably from about 30 percent to about 50 percent, based on the weight of the isoparaffins component in the mixture, of isoparaffins which are of a multi-methyl branched species (e.g., dimethyl, trimethyl, etc.), or contains one or more branches of carbon number higher than methyl (e.g., ethyl, propyl, etc.), or both. The base oil composition has a molar isoparaffin:n-paraffin ratio ranging from about 0.5:1 to about 9:1, preferably from about 1:1 to about 3:1, and boils within a range of from about 320xc2x0 F. to about 700xc2x0 F., preferably from about 500xc2x0 to about 700xc2x0 F. The presence of these concentrations of multi-methyl branched isoparaffins, or isoparaffins with branches of higher carbon number than methyl in the mixture effectively increases the low temperature performance of a drilling fluid made from such base oil thereby enabling use of the drilling fluid under cold temperature conditions; and yet, the drilling fluid retains its desirable high performance and outstanding environmental characteristics.
The C10-C24, or C12-C18 solvent composition of the drilling fluid, or drilling mud, in all embodiments constitutes, a continuous liquid phase, or continuous invert emulsion phase where water or brine is present and emulsified within the solvent composition. Where water is present, the solvent:water volume ratio generally ranges from about 90:10 to about 60:40; preferably from about 80:20 to about 70:30.
The continuous, or invert emulsion phase of the drilling fluid, or drilling mud, of this invention is emulsified by dispersing therein at least one additive selected from the group consisting of weighting agents, emulsifiers, wetting agents, viscosifiers, fluid loss control agents, proppants for use in fracturing subterranean formations, and particulate agents as used in gravel packs.
In forming the drilling fluid, or mud, generally one or more of the weighting agents, emulsifiers, wetting agents, viscosifiers, fluid loss control agents, proppants, and particulate agents are mixed with the paraffinic solvent composition to form an emulsion in which the latter forms a continuous oil phase, or water-in-oil invert emulsion phase. In such systems, the high purity solvent composition constitutes generally from about 50 percent to about 95 percent, and more often-and preferably, from about 60 percent to about 80 percent of the total drilling fluid, or mud, based on the total volume of the composition; with the balance of the drilling fluid, or mud, being water, brine or other additive, or additives. A drilling fluid, or mud, of this character provides excellent rheological properties under a wide variety of drilling conditions. Exemplary of additives useful in the practice of this invention are: weighting materials such as barite, iron oxide, calcium oxide, etc.; emulsifiers such as fatty acids, soaps of fatty acids, and fatty acid derivatives such as a amido-amines, polyamides, polyamines, esters, e.g., sorbitan monoleate polyethoxylate, etc.; wetting agents such as crude tall oil, organic phosphate esters, modified imidazolines and amido-amines, alkyl aromatic sulfates and sulfonates, etc.; viscosifiers such as organophilic clays, oil soluble polymers, polyamide resins, polycarboxylic acids and soaps, etc.; fluid loss control materials such as modified lignites, polymers, asphaltic compounds and the like, etc.; proppant materials such as sand grains, walnut shells, etc.; gravel and the like. Water, or brine, as suggested, can also be present in or added to the drilling fluid, or mud. Typically, the weighting agent is added in concentrations ranging up to about 18 pounds per barrel of paraffinic solvent; the emulsifiers and wetting agents, respectively, in concentrations ranging from about 2 to about 6 pounds, per barrel of paraffinic solvent; the viscosifiers in concentrations ranging from about 1 to about 10 pounds per barrel of paraffinic solvent; and the fluid loss control agents in concentrations ranging from about 1 to about 20 pounds per barrel of paraffinic solvent.
The paraffinic oil base, or solvent, component for the drilling fluid, or mud, can be obtained from a Fischer-Tropsch reaction product or wax, or from slack waxes which serve as feeds for the production of the solvent component of the mud. The solvent component is produced by the hydrocracking and hydroisomerization of C5+ paraffinic, or waxy hydrocarbon feeds, especially Fischer-Tropsch waxes, or reaction products at least a fraction of which boils above 700xc2x0 F., i.e., at 700xc2x0 F.+. The waxy feed is contacted, with hydrogen, over a dual functional catalyst to produce hydroisomerization and hydrocracking reactions sufficient to convert at least about 20 percent to about 90 percent, preferably from about 30 percent to about 80 percent, on a once through basis based on the weight of the 700xc2x0 F.+ feed component, or 700xc2x0 F.+ feed, to 700xc2x0 F.xe2x88x92 materials, and produce a liquid product boiling from about 74xc2x0 F. to about 1050xc2x0 F., i.e., a C5-1050xc2x0 F. liquid product, or crude fraction. The C5-1050xc2x0 F. crude fraction is topped via atmospheric distillation to produce two fractions, (i) a low boiling fraction having an initial boiling point ranging between about 74xc2x0 F. and about 100xc2x0 F., and an upper end boiling point of about 700xc2x0 F., and (ii) a high boiling fraction having an initial boiling point of about 700xc2x0 F., and an upper end boiling point of about 1050xc2x0 F., or higher, i.e., 1050xc2x0 F.+. The low boiling fraction (i), or fraction boiling between about C5 and about 700xc2x0 F., which is constituted substantially of paraffins, provides a material from which the solvent component of the drilling fluid or mud, can be recovered, or the solvent component for the drilling fluid, or mud, may be obtained from slack waxes. Slack waxes are the by-products of dewaxing operations where a diluent such as propane or a ketone (e.g., methylethyl ketone, methyl isobutyl ketone) or other diluent is employed to promote wax crystal growth, the wax being removed from the lubricating oil base stock by filtration or other suitable means. The slack waxes are generally paraffinic in nature, boil above about 600xc2x0 F., preferably in the range of 600xc2x0 F. to about 1050xc2x0 F., and may contain from about 1 to about 35 wt. % oil. Waxes with low oil contents, e.g., 5-20 wt. % are preferred; however, waxy distillates or raffinates containing 5-45% wax may also be used as feeds. Slack waxes are usually freed of polynuclear aromatics and hetero-atom compounds by techniques known in the art; e.g., mild hydrotreating as described in U.S. Pat. No. 4,900,707, which also reduces sulfur and nitrogen levels preferably to less than 5 ppm and less than 2 ppm, respectively. Fischer-Tropsch waxes are preferred feed materials, having negligible amounts of aromatics, sulfur and nitrogen compounds. The Fischer-Tropsch liquid, and wax, is characterized as the product of a Fischer-Tropsch process wherein a synthetic gas, or mixture of hydrogen and carbon monoxide, is processed at elevated temperature over a supported catalyst comprised of a Group VIII metal, or metals, of the Periodic Table of The Elements (Sargent-Welch Scientific Company, Copyright 1968), e.g., cobalt, ruthenium, iron, etc. The Fischer-Tropsch liquid contains C5+, preferably C10+, more preferably C20+ paraffins. A distillation showing the fractional make up (xc2x110 wt. % for each fraction) of a typical Fischer-Tropsch product is as follows:
A 700xc2x0 F.+ wax feed, or wax feed containing 700xc2x0 F.+ hydrocarbons, preferably the former, is contacted, with hydrogen, at hydrocracking/ hydroisomerization conditions over a bifunctional catalyst, or catalyst containing a metal, or metals, hydrogenation component and an acidic oxide support component active in producing both hydrocracking and hydroisomerzation reactions. Preferably, a fixed bed of the catalyst is contacted with the feed at conditions which convert about 20 to 90 wt. %, preferably about 30 to 80 wt. % of the 700xc2x0 F.+ feed (or 700xc2x0 F.+ component of the feed) to a low boiling fraction having an initial boiling point of about C5 (about 74xc2x0 F. to about 100xc2x0 F.) and an end boiling point of about 700xc2x0 F., and a higher boiling fraction having an initial boiling point corresponding to the upper end boiling point of the low boiling fraction and a higher end boiling point of 1050xc2x0 F., or greater. In general, the hydrocracking/hydroisomerization reaction is conducted by contacting the waxy feed over the catalyst at a controlled combination of conditions which produce these levels of conversion, e.g., by selection of temperatures ranging from about 400xc2x0 F. to about 850xc2x0 F., preferably from about 500xc2x0 F. to about 700xc2x0 F., pressures ranging generally from about 100 pounds per square inch gauge (psig) to about 1500 psig, preferably from about 300 psig to about 1000 psig, hydrogen treat gas rates ranging from about 1000 SCFB to about 10,000 SCFB, preferably from about 2000 SCFB to about 5000 SCFB, and space velocities ranging generally from about 0.5 LHSV to about 10 LHSV, preferably from about 0.5 LHSV to about 2 LHSV. Optionally, and preferably, after the hydrocracking/hydroisomerization step is completed, the high purity solvent composition that is recovered, and which is to be used as a component of the drilling fluid, or mud, is subjected to a mild hydrotreating step to ensure that the finished product is free of aromatics.
The active metal component of the catalyst used in the hydrocracking/hydroisomerization reaction is preferably a Group VIII metal, or metals, of the Periodic Table Of The Elements (Sargent-Welch Scientific Company Copyright 1968) in amount sufficient to be catalytically active for hydrocracking and hydroisomerization of the waxy feed. The catalyst may also contain, in addition to the Group VIII metal, or metals, a Group IB and/or a Group VIB metal, or metals, of the Periodic Table. Generally, metal concentrations range from about 0.05 percent to about 20 percent, based on the total weight of the catalyst (wt. %), preferably from about 0.1 wt. percent to about 10 wt. percent. Exemplary of such metals are the non-noble Group VIII metals such as nickel and cobalt, or mixtures of these metals with each other or with other metals, such as copper, a Group IB metal, or molybdenum, a Group VIB metal. Palladium and platinum are exemplary of suitable Group VIII noble metals. The metal, or metals, is incorporated with the support component of the catalyst by known methods, e.g., by impregnation of the support with a solution of a suitable salt or acid of the metal, or metals, drying and calcination.
The catalyst support is constituted of metal oxide, or metal oxides, components at least one component of which is an acidic oxide active in producing olefin cracking and hydroisomerization reactions. Exemplary oxides include silica, silica-alumina, clays, e.g., pillared clays, magnesia, titania, zirconia, halides, e.g., chlorided alumina, and the like. The catalyst support is preferably constituted of silica and alumina, a particularly preferred support being constituted of up to about 35 wt. % silica, preferably from about 2 wt. % to about 35 wt. % silica, and having the following porestructural characteristics:
The base silica and alumina materials can be, e.g., soluble silica containing compounds such as alkali metal silicates (preferably where Na2O:SiO2=1:2 to 1:4), tetraalkoxy silane, orthosilic acid ester, etc.; sulfates, nitrates, or chlorides of aluminum alkali metal aluminates; or inorganic or organic salts of alkoxides or the like. When precipitating the hydrates of silica or alumina from a solution of such starting materials, a suitable acid or base is added and the pH is set within a range of about 6.0 to 11.0. Precipitation and aging are carried out, with heating, by adding an acid or base under reflux to prevent evaporation of the treating liquid and change of pH. The remainder of the support producing process is the same as those commonly employed, including filtering, drying and calcination of the support material. The support may also contain small amounts, e.g., 1-30 wt. %, of materials such as magnesia, titania, zirconia, hafnia, or the like.
Support materials and their preparation are described more fully in U.S. Pat. No. 3,843,509 incorporated herein by reference. The support materials generally have a surface area ranging from about 180-400 m2/g, preferably 230-375 m2/g, a pore volume generally of about 0.3 to 1.0 ml/g, preferably about 0.5 to 0.95 ml/g, bulk density of generally about 0.5-1.0 g/ml, and a side crushing strength of about 0.8 to 3.5 kg/mm.
The following examples are illustrative of the more salient features of this invention. All parts, and percentages, are given in terms of weight unless otherwise specified.